We propose to study the ability of uniform electric fields to terminatesingle self-sustaining spiral rotors, such as those associated with many cardiac arrhythmias. We hypothesize that the strength of the electric field necessary to terminate a rotor varies with (a) the phase of the rotor with respect to the field direction, and (b) the direction of the field with respect to the tissue fiber direction. To test these hypotheses, we have developed a large-scale supercomputer model suitable for the detailed study of the initiation, maintenance, and termination of two-dimensional spiral rotors. The results obtained from this study may have direct implications for improving the efficiency and efficacy of the delivery of life-saving defibrillation shocks to patients in cardiac arrest.